CN109808508B - A fault-tolerant control strategy for the drive system of a distributed drive electric vehicle - Google Patents

Abstract

The invention discloses a fault-tolerant control strategy of a driving system of a distributed driving electric automobile, which is used for carrying out fault-tolerant control on a vehicle under the condition that a certain wheel is known to be invalid; and (3) upper layer control: selecting yaw velocity and mass center deflection angle of the vehicle as control targets, establishing a vehicle yaw moment control system under failure fault, and calculating to obtain an expected yaw moment through a sliding mode variable structure control strategy based on constraint of the yaw velocity and the mass center deflection angle; and (3) controlling the lower layer: the dynamic and stability torque coordination optimization distribution strategy is realized through sliding mode variable structure control or LQR respectively, the distribution of wheel torque is calculated by combining the expected yaw moment, the torque redistribution is carried out on the wheels which normally work, and the driving stability of the vehicle is ensured. The invention can redistribute the moment of wheels which normally work, and the wheels can meet the preset driving track to the maximum extent, thereby avoiding sudden change and ensuring the safety and stability of vehicle driving.

Description

A fault-tolerant control strategy for the drive system of a distributed drive electric vehicle

technical field

The invention relates to the field of distributed drive electric vehicle control, in particular to a fault-tolerant control strategy for a drive system of a distributed drive electric vehicle.

Background technique

Under the current environmental situation, electric vehicles are the focus and focus of research in the automotive industry. Distributed drive electric vehicle is a kind of electric vehicle. It has the advantage that four wheels can be driven independently, which makes it easier to control the longitudinal force of each tire. When failure occurs, distributed drive electric vehicle can better reduce the harm caused by failure. and losses.

The existing stability or dynamic control strategies are generally based on vehicles under normal driving conditions, and there are few patents on fault-tolerant control strategies applicable to failures. If there is a sudden drive failure during the driving process of the vehicle, if the fault-tolerant control is not carried out in time, it will seriously affect the driving safety.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a fault-tolerant control strategy for a drive system of a distributed drive electric vehicle, aiming at the defects in the prior art.

The technical scheme adopted by the present invention to solve its technical problems is:

The invention provides a fault-tolerant control strategy for a drive system of a distributed driving electric vehicle. In the drive system of the electric vehicle, the upper controller adopts sliding mode variable structure control, and the lower controller adopts sliding mode variable structure control or LQR; the fault-tolerant control strategy Include the following steps:

When a certain wheel is known to fail, the fault-tolerant control strategy is used to carry out the fault-tolerant control of the vehicle;

Upper-level control: The yaw rate and the deflection angle of the center of mass of the vehicle are selected as the control targets, and the vehicle yaw moment control system under failure fault is established. Through the sliding mode variable structure control strategy constrained based on the yaw rate and the deflection angle of the center of mass, the expectation is calculated. yaw moment;

Lower layer control: through sliding mode variable structure control or LQR to realize the coordinated optimal distribution strategy of dynamic and stability torque, combined with the expected yaw moment, calculate the distribution of wheel torque, and redistribute the torque to the normal working wheels to ensure the vehicle driving stability.

Further, in the upper layer control of the present invention, the sliding mode variable structure control is used to obtain the desired yaw moment of the vehicle; an additional yaw moment controller is designed, and the sliding mode variable structure control is used to obtain the desired additional yaw moment M; The declination angle β and the yaw angular velocity γ are used as state variables, the input is the error between the vehicle's center of mass slip angle β and the yaw angular velocity γ and the actual value, and the output is M, the formula is as follows:

s=e _γ -c·e _β =γ _d -γ+c·(β _d -β)

可得：by

Available:

in,

Among them, c and ε are the design parameters of the controller, β is the side-slip angle of the center of mass, β _d is the expected side-slip angle of the center of mass, γ is the yaw angular velocity, γ _d is the expected yaw angular velocity, m is the curb weight of the vehicle, v _x is the longitudinal vehicle speed, F _yf and F _yr are the lateral forces of the front and rear wheels of the vehicle, δ _f is the front wheel rotation angle, α _f , α _r are the front and rear wheel slip angles, l _f , l _r are the center of mass to the front and rear axles distance, k _f and k _r are the cornering stiffness of the front and rear wheels, and I _Z is the moment of inertia of the vehicle around the Z axis.

Further, the lower layer control of the present invention adopts the coordinated optimal distribution strategy of dynamics and stability torque, realizes two control strategies through sliding mode variable structure control or LQR, and realizes software redundancy to reduce software errors.

Further, the concrete method of adopting the sliding mode variable structure control strategy in the lower layer control of the present invention is:

In the upper layer control, the sliding mode variable structure control is used to obtain the desired driving moment T; first, the relationship between the additional yaw moment M and the longitudinal slip rate λ is established: through the dynamic equation, the relationship between the additional yaw moment M and the tire longitudinal force F _x is obtained , and then look up the table by the magic formula to obtain the corresponding slip rate λ, so that the desired additional yaw moment obtained by the upper controller is converted to obtain the longitudinal slip rate λ; through the slip rate, the relationship between λ and T is established; The longitudinal slip rate λ is the state variable, and the error between the expected value and the actual value is used as the control input, and the driving torque is finally obtained; its calculation formula is:

in

where λ is the longitudinal slip rate, λ _d is the desired longitudinal slip rate, q is the design parameter of the sliding mode controller, v _x is the longitudinal vehicle speed, ω is the vehicle rotational angular velocity, R is the wheel radius, T _t is the driving torque, μ is the road adhesion coefficient, F _z is the vertical load of the vehicle, J is the moment of inertia of the wheel, and g is the gravitational acceleration.

Further, the concrete method that adopts the LQR control strategy in the lower layer control of the present invention is:

LQR is used to control the torque distribution after failure, and the desired yaw moment is generated by applying different driving forces to the four independently driven wheels. The following formula is the torque required by the four wheels obtained after the torque distribution is controlled according to the LQR Variation:

Among them, M is the additional yaw moment obtained by the upper controller, R is the wheel radius, d _f and d _r are the front and rear wheelbases, l _f and l _r are the distances from the center of mass to the front and rear axles, and δ _f is the front and rear axles. Turning angle.

Further, the dynamic and stability torque coordination optimization distribution strategy in the lower layer control of the present invention, according to the vehicle driving theory, adds longitudinal driving force, can provide maximum driving force, and maximum ground adhesion as the constraints:

Tire Friction Ellipse Limits:

Road adhesion and the limit of longitudinal force that can provide maximum driving force:

max(-μF _zi ,-F _m )≤F _xi ≤min(μF _zi ,F _m )

Among them, F _xi is the wheel longitudinal force, F _yi is the wheel lateral force, F _zi is the wheel vertical load, μ is the road adhesion coefficient, and F _m is the maximum wheel longitudinal force.

The beneficial effects of the present invention are: the fault-tolerant control strategy of the drive system of the distributed drive electric vehicle of the present invention performs fault-tolerant control for the drive failure problem that occurs during the driving process of the vehicle, and the upper layer obtains the desired yaw moment according to the sliding mode variable structure control, The lower layer gets the torque distributed to each wheel through sliding mode variable structure control or LQR (Linear Quadratic Regulator). The torque redistribution is performed on the normal working wheels, which may conform to the predetermined driving trajectory to the greatest extent, avoid sudden changes, and ensure the safety and stability of the vehicle.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and examples, in which:

1 is a schematic structural diagram of an embodiment of the present invention;

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

As shown in FIG. 1, the fault-tolerant control strategy of the drive system of the distributed drive electric vehicle according to the embodiment of the present invention, in the drive system of the electric vehicle, the upper controller adopts sliding mode variable structure control, and the lower controller adopts sliding mode variable structure control Or LQR; this fault-tolerant control strategy includes the following steps:

When a certain wheel is known to fail, the fault-tolerant control strategy is used to carry out the fault-tolerant control of the vehicle;

Upper-level control: The yaw rate and the deflection angle of the center of mass of the vehicle are selected as the control targets, and the vehicle yaw moment control system under failure faults is established. Through the sliding mode variable structure control strategy constrained based on the yaw rate and the deflection angle of the center of mass, the expected yaw moment;

Lower layer control: through sliding mode variable structure control or LQR to realize the coordinated optimal distribution strategy of dynamic and stability torque, combined with the expected yaw moment, calculate the distribution of wheel torque, and redistribute the torque to the normal working wheels to ensure the vehicle driving stability.

Assuming that the longitudinal force of each vehicle can be detected, the present invention performs fault-tolerant control when a certain wheel is known to fail. The upper controller performs sliding mode control according to the difference between the yaw rate and the center of mass slip angle to obtain the desired yaw moment. When the lower layer implements the control, the wheel torque distribution is determined by the yaw moment.

The upper layer inputs the actual yaw rate and the center of mass slip angle, calculates the expected yaw moment M through the sliding mode formula, and then inputs it to the lower layer controller.

s=e _γ -c·e _β =γ _d -γ+c·(β _d -β)

可得：by

Available:

The lower input is the desired yaw moment M.

(1) Taking the sliding mode variable structure control as an example, the input is the expected yaw moment M, and the relationship between M and the longitudinal force F _xij can be obtained from the vehicle dynamics model:

M=F _xfl ·(sinδ _f ·l _f -d ·cosδ _f /2)+F _xfr ·(sinδ _f ·l _f +d ·cosδ _f /2)-F _xrl ·d/2+F _xrr ·d/ 2 According to the obtained expected yaw moment, the expected longitudinal force can be obtained, and then the expected slip rate λ can be obtained by looking up the table from the tire formula, and then input into the sliding mode controller for further solution.

这样就可以得到车轮应有的输出转矩。in

In this way, the proper output torque of the wheel can be obtained.

(2) Taking LQR control as an example, calculate the torque ΔT _ij that the wheel needs to change, and then adjust the torque of the normal working wheel according to the failure situation.

Among them, M is the additional yaw moment obtained by the upper controller, R is the wheel radius, d _f and d _r are the front and rear wheelbases, l _f and l _r are the distances from the center of mass to the front and rear axles, and δ _f is the front and rear axles. Turning angle.

If the left front wheel fails,

Then the expected torque of the right front wheel is:

Then the expected torque of the right rear wheel is:

Then the expected torque of the left rear wheel is:

If other wheels fail, there are corresponding algorithms.

Two lower-level control strategies can achieve software redundancy, and if one of them has a large deviation, the other can be compensated.

It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention.

Claims (2)

1. A fault-tolerant control strategy of a driving system of a distributed driving electric automobile is characterized in that in the driving system of the electric automobile, an upper-layer controller adopts sliding mode variable structure control, and a lower-layer controller adopts sliding mode variable structure control or LQR; the fault-tolerant control strategy comprises the following steps:

under the condition that a certain wheel is known to be invalid, fault-tolerant control of the vehicle is carried out by adopting a fault-tolerant control strategy;

and (3) upper layer control: selecting yaw velocity and mass center deflection angle of the vehicle as control targets, establishing a vehicle yaw moment control system under failure fault, and calculating to obtain an expected yaw moment through a sliding mode variable structure control strategy based on constraint of the yaw velocity and the mass center deflection angle;

and (3) controlling the lower layer: the dynamic and stability torque coordination optimization distribution strategy is realized through sliding mode variable structure control or LQR respectively, the distribution of wheel torque is calculated by combining an expected yaw moment, the torque redistribution is carried out on wheels which normally work, and the driving stability of the vehicle is ensured;

in the upper layer control, the sliding mode variable structure control is adopted to obtain the expected yaw moment of the vehicle; an additional yaw moment controller is designed, and a sliding mode variable structure is used for controlling to obtain an expected additional yaw moment M; selecting a centroid side slip angle beta and a yaw velocity gamma as state variables, inputting the errors of the centroid side slip angle beta and the yaw velocity gamma of the vehicle and actual values, and outputting the errors as M, wherein the formula is as follows:

s＝e_γ-c·e_β＝γ_d-γ+c·(β_d-β)

and is composed of

The following can be obtained:

wherein,

wherein c and epsilon are design parameters of the controller, beta is a centroid slip angle, and beta_dTo the desired centroid slip angle, gamma is the yaw rate, gamma_dPeriod of time ofThe expected yaw angular velocity, m is the overall vehicle servicing quality, v_xFor longitudinal vehicle speed, F_yf、F_yrTransverse forces, δ, of the front and rear wheels of the vehicle_fAngle of rotation of front wheel, α_f、α_rIs a front and rear wheel side slip angle l_f、l_rIs the distance of the center of mass to the front and rear axes, k_f、k_rFor front and rear wheel cornering stiffness, I_ZThe moment of inertia of the vehicle around the Z axis;

in the lower-layer control, a dynamic and stable torque coordination optimization distribution strategy is adopted, two control strategies are realized through sliding mode variable structure control or LQR, software redundancy is realized, and the condition of software errors is reduced;

the specific method for adopting the sliding mode variable structure control strategy in the lower layer control comprises the following steps:

in the upper layer control, a desired driving moment T is obtained by using sliding mode variable structure control; firstly, establishing a relation between an additional yaw moment M and a longitudinal slip ratio lambda: obtaining an additional yaw moment M and a tire longitudinal force F through a dynamic equation_xThe corresponding slip rate lambda is obtained by looking up a table through a magic formula, so that the expected additional yaw moment obtained by the upper-layer controller is converted to obtain the longitudinal slip rate lambda; establishing the relation between lambda and T through the slip ratio; selecting a longitudinal slip ratio lambda as a state variable, and taking an error between a desired value and an actual value as a control input to finally obtain a driving torque; the calculation formula is as follows:

wherein

Wherein λ is longitudinal slip ratio, λ_dQ is a sliding mode controller design parameter, v, for a desired longitudinal slip ratio_xFor longitudinal vehicle speed, ω is vehicle angular velocity, R represents wheel radius, T_tRepresenting the driving torque, mu being the road adhesion coefficient, F_zThe vertical load of the vehicle is represented by J, the moment of inertia of the wheel is represented by g, and the gravity acceleration is represented by g;

the specific method for adopting the LQR control strategy in the lower-layer control comprises the following steps:

the moment distribution after failure is controlled by the LQR, the expected yaw moment is generated by applying driving forces with different magnitudes to four independently driven wheels, and the following formula is the moment variation quantity required by the four wheels obtained by controlling the moment distribution according to the LQR:

where M is the additional yaw moment obtained by the upper level controller, R represents the wheel radius, d_f、d_rFor front and rear wheelbases, /)_f、l_rIs the distance of the center of mass to the front and rear axes, δ_fIs the corner of the front wheel.

2. The fault-tolerant control strategy of the driving system of the distributed driving electric automobile according to claim 1, characterized in that a dynamic and stability torque coordination optimization distribution strategy in the lower layer control adds longitudinal driving force, can provide maximum driving force and takes the maximum ground adhesion as the constraint condition aiming at the vehicle driving theory:

tire friction ellipse limit:

road adhesion and limitation of longitudinal force to be able to provide maximum driving force:

max(-μF_zi,-F_m)≤F_xi≤min(μF_zi,F_m)

wherein, F_xiAs longitudinal force of the wheel, F_yiAs lateral wheel forces, F_ziIs the vertical wheel load, mu is the road adhesion coefficient, F_mIs the maximum value of the wheel longitudinal force.

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